I have never heard of them hiding serial numbers before. Where did you get the bass? Have you checked all over the bridge? If I recall the serial number was under the strings just before the holes to enter the bridge. Make sure you look thoroughly.

If you cannot find it I am at a loss. Are you SURE it's a sterling musicman bass? Is it possible the bolt plate for the neck was replaced? Did you buy it new? Give us some info.

Older Music Man basses have the serial number stamped on the bridge, newer ones after 1996 or so, have it on the neck plate. If for some reason the neck plate was replaced, under Ernie Ball policy, it cannot be replaced with another serialized plate, therefore all is lost.

It is a real Musicman Bass I bought in a music shop..
There are musicman logos on the neck, brigge, tuners, back etc..
IT IS A REAL ONE !
No doubt about it.
I think the number is maybe above the pickguard or between the neck and the body..
ARG ! DOES ANYBODY GOT A STERLING !?